The present invention is related to the field of bioelectrical circuit analyzers, and more specifically to bioelectrical circuit analyzers capable of identifying and categorizing various biomolecules and biomolecular complexes by electrical parameter analysis thereof.
Detection of antigens such as viruses and bacteria is critical for medical diagnoses. Currently, the commonly used methods for immunological tests include enzyme-linked immunosorbent assay (ELISA) and immunoradiometric assay (IRMA). However, these multi-step techniques tend to be tedious and expensive. Hence, there is considerable effort directed towards development of microsensors, in particular immunosensors that can allow quick and precise detection of molecules.
Identification of biomolecular complexes also is advantageous in research, e.g. pharmaceutical research and development. As one example, a gene regulatory protein can be identified by its ability to bind to a specific deoxyribonucleic acid sequence. Current methods for detecting such complexes include radiometric, fluorometric and chromogenic assays. Such assays provide only a binary yes-no answer and cannot provide more advanced data, such as differentiation among different binding species.
Electrical detection methods have been based on potentiometric, piezoelectric, and capacitive systems. Potentiometric systems measure the variation in the surface potential of an electrode or change in drain current of a transistor. These measurements tend to be non-specific. Piezoelectric systems measure the change in the mass of molecules bound to a quartz surface, but suffer from instabilities and problems with calibration.
Capacitive measurements have been used for detection of DNA and cell structures, such as U.S. Pat. No. 5,891,630 (Eggers et al.); U.S. Pat. No. 6,169,394 (Frazier et al.); and U.S. Pat. No. 5,846,708 (Hollis et al.). In these studies, the substrates have consisted of Si/SiO2 or metal electrodes coated with insulating material. These approaches further have focused on determination of a unique “resonance frequency” for a given molecule or complex.
Capacitive detection of antibodies and antigens bound to a sensor surface has been reported. However, these electrical detection approaches have employed only a fixed frequency to detect relative changes in the dielectric constant due to binding to the sensor surface.